Cebpa interacts with E2f1 bound to promoters (Slomiany et al. 2000, Porse et al. 2001). Cebpa inhibits the transcriptional activation activity of E2f1. The N terminus of the p42 isoform of Cebpa is required for interaction with E2f factors (Porse et al. 2001) and therefore the p30 isoform, which lacks the N terminus, has a reduced ability to inhibit proliferation.